We're overlapped on the same tack — can the leeward boat head up on me?
Yes, as long as she stays at or below her own proper course. Under Rule 11 the windward boat must keep clear of the leeward boat. Heading up to sail inshore out of the tide can be the leeward boat's proper course, so Rule 17 doesn't stop her — and the windward boat, with room and time to keep clear, must do so. (World Sailing Case 14.)
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<p><a href="https://sailing.kiwi.nz/run/case-14-leeward-can-head-up/">Source: Sailing Kiwi</a></p>